Apparatus for scraping excess coating substance off a running web

Abstract

An apparatus and process are disclosed for scraping excess coating substance from a running web by moving the web past a scraper blade that is oriented transversely to the running direction of the web. The blade is pressed against the web with a variable force. A motor automatically moves the blade to maintain the angle between the scraping surface thereof and the web approximately constant when the force varies, preferably by rotating the blade about an axis which is located near the scraping surface, is transverse to the running direction of the web and extends generally parallel to the blade direction of extension across the web. The amount of movement of the blade that is necessary to maintain the angle constant is preferably determined by monitoring either the thickness of the coating on the web or the degree to which the force on the blade deforms the blade from an undeformed shape. The automatic system can preferably be disabled to permit the blade angle to be set at a selected value manually.

What is claimed is: 
     
       1. Apparatus for scraping excess coating substance off a running web, comprising: a scraper blade extending across the web transverse to the running direction thereof and having a free end portion with a scraping surface;   means for running a web coated with a coating substance past the scraping surface for the scraping surface to scrape excess coating substance off the web;   pressure means for exerting a force on the blade for pressing the scraping surface against the web;   means for supporting the blade at a distance from the free end portion of the blade and for moving the blade, through movement of this means, for adjusting the blade angle between the blade, at the free end portion thereof, and the web; the moving means being adapted to rotate the blade about an axis of rotation transverse to the running direction of the web, and the rotation axis being located near the free end portion of the blade;   means for monitoring a selected parameter representative of the blade angle between the blade, in the vicinity of the free end portion, and the web; and   control means connected with the moving means for causing the blade to be rotated about the axis of rotation by the moving means responsive to changes in the value of the parameter being monitored, to maintain the blade angle between the blade and the web approximately constant.   
     
     
       2. The apparatus of claim 1, wherein the means for moving the blade comprise a motor and connector means for transmitting force from the motor to the blade. 
     
     
       3. The apparatus of claim 2, wherein the monitoring means measures a parameter that is the thickness of the coating on the web, and wherein the control means further comprises means for actuating the motor for moving the blade whenever the measured thickness of the coating varies from a predetermined value. 
     
     
       4. The apparatus of claim 1, further comprising disconnect switch means for disabling the control means from causing movement of the blade. 
     
     
       5. The apparatus of claim 4, further comprising means for locking the blade in a selected position such that the blade angle is zero, when the disconnect switch means disables the control means. 
     
     
       6. The apparatus of claim 5, wherein the means for moving the blade comprises a motor, and wherein the means for locking the blade in place at a blade angle of zero comprises gear means cooperating with the motor and the blade to transmit force from the motor to the blade when the motor is actuated. 
     
     
       7. The apparatus of claim 1, wherein the pressure means comprise a pressure element for being pressed against the blade to press the blade against the web. 
     
     
       8. The apparatus of claim 7, wherein the blade has a support point at which it is supported, and wherein the pressure element presses against the blade at a location between the scraping surface of the blade and the support point of the blade. 
     
     
       9. The apparatus of claim 1, wherein the pressure means further comprises: a pressure element holder; a pressure element secured to the pressure element holder and in contact with the blade for exerting a force thereon; and   blade holder means to which the pressure element holder is attached.   
     
     
       10. The apparatus of claim 9, wherein the pressure element holder is attached for rotation relative to the blade holder means about a second axis of rotation parallel to the scraping surface of the blade and transverse to the running direction of the web, rotation of the pressure element holder about the second axis of rotation serving to vary the force with which the scraping surface of the blade presses against the web. 
     
     
       11. The apparatus of claim 10, wherein the monitoring means comprises first and second pressurized gas hoses cooperating with the blade holder means and the pressure element holder to cause rotation of the pressure element holder about the second axis of rotation when the gas pressure in the first gas hose varies; the monitoring means further comprising means for supplying pressurized gas to the pressurized gas hoses and for varying the pressure in the first pressurized gas hose. 
     
     
       12. The apparatus of claim 11, wherein the pressure element holder has a projecting tail portion, and wherein the blade holder means comprises an end portion defining a recess into which the tail portion of the pressure element holder projects; and wherein the first and second pressurized gas hoses are disposed side-by-side in the recess defined by the end portion of the blade holder means and are spaced apart in the recess by the tail portion of the pressure element holder, the diameter of the first pressurized gas hose varying responsive to variations in the gas pressure in the first hose, and variations in the diameter of the first pressurized gas hose serving to displace the tail portion of the pressure element holder and thereby to cause the pressure element holder to rotate about the second axis of rotation. 
     
     
       13. The apparatus of claim 12, wherein the means for supplying pressurized gas further comprises a pressure regulating valve for controlling the gas pressure in the first pressurized gas hose. 
     
     
       14. The apparatus of claim 13, wherein the control means further comprises a regulating device for controlling the pressure regulating valve. 
     
     
       15. The apparatus of claim 14, wherein the monitoring means further comprises means for measuring the thickness of the coating on the web, and wherein the thickness of the coating is the parameter being monitored by the monitoring means. 
     
     
       16. The apparatus of claim 14, wherein the regulating device generates a control signal to control the pressure regulating valve, thereby to control the force exerted on the blade by the pressure means, and wherein the control means further comprises signal processor means for generating an adjustment signal responsive to the control signal, the adjustment signal actuating the means for moving the blade to maintain the angle between the scraping surface of the blade and the web approximately constant. 
     
     
       17. The apparatus of claim 16, further comprising disconnect switch means for disabling the signal processor means, thereby to prevent movement of the blade responsive to changes in the parameter being monitored. 
     
     
       18. The apparatus of claim 14, wherein the regulating device controls the pressure regulating valve to cause the pressure means to exert a predetermined force on the blade. 
     
     
       19. The apparatus of claim 12, wherein the means for moving the blade comprises a motor, and wherein the monitoring means further comprises means for monitoring the difference in gas pressure between the first and second pressurized hoses and for actuating the motor to move the blade responsive to variations in the pressure difference from a preselected value. 
     
     
       20. The apparatus of any of claims 1, 12 or 16, wherein the monitoring means further comprises means for measuring the extent to which the shape of the blade is deformed from a relatively undeformed shape which it has when it does not press against the web, and wherein the parameter monitored by the monitoring means is the shape of the blade as it is deformed by the force exerted on it by the pressure means. 
     
     
       21. The apparatus of claim 20, wherein the monitoring means further comprises strain gauge means to monitor the shape of the blade as it is deformed by the force exerted on it by the pressure means. 
     
     
       22. The apparatus of claim 20, wherein the monitoring means further comprises optical scanning means for monitoring the shape of the blade as it is deformed by the force exerted on it by the pressure means. 
     
     
       23. The apparatus of either of claims 1 or 12, wherein the means for running the web past the blade comprises a roller around which the web is run.